Migration and agglomeration imaging method

ABSTRACT

A migration imaging method is disclosed which comprises providing an imaging member comprising a substrate, a layer of softenable material containing a layer of photosensitive material and an overlayer of material on the softenable material comprising a partially esterfied rosin polymer. This member is uniformly negatively charged, heated sufficiently to allow substantially all the negative charge on the surface of the overlayer to migrate in depth in the overlayer, and then cooled to its original temperature, uniformly negatively charged a second time, and then imagewise exposed to activating electromagnetic radiation. The member is then heat developed whereby the imagewise exposed migration material migrates in image configuration through the softenable material to the substrate and the unexposed migration material simultaneously agglomerates and migrates in depth in the softenable material.

United States Patent [191 Sankus, Jr.

[ Aug. 26, 1975 MIGRATION AND AGGLOMERATION IMAGING METHOD Joseph G. Sankus, Jr., McKinney, Tex.

[75} Inventor:

[73] Assignee: Xerox Corporation, Stamford,

Conn.

221 Filed: July 24, 1974 [21] Appl. No: 491.578

Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, or Firm-J. J. Ralabate; D. C. Petre; R. L. Lyons 15 7 1 ABSTRACT A migration imaging method is disclosed which comprises providing an imaging member comprising a substrate, a layer of softenable material containing a layer of photosensitive material and an overlayer of material on the softenable material comprising a partially esterfied rosin polymer. This member is uniformly negatively charged, heated sufficiently to allow substantially all the negative charge on the surface of the overlayer to migrate in depth in the overlayer, and then cooled to its original temperature, uniformly negatively charged a second time and then imagewise exposed to activating electromagnetic radiation. The member is then heat developed whereby the imagewise exposed migration material migrates in image configuration through the softenable material to the substrate and the unexposed migration material simultaneously agglomerates and migrates in depth in the softenable material.

6 Claims, 7 Drawing Figures PATENTED MJE 2 6 I975 IO 2m F/6.3 a

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MIGRATION AND AGGLOMERATION IMAGING METHOD BACKGROUND OF THE INVENTION This invention relates generally to migration imaging systems, and more specifically, to a process of migration imaging wherein the migration imaging member is developed to allow imagewise migration of the migration material through the softenable material to the substrate and simultaneous agglomeration and migration in depth in the softenable material of the unexposed migration material.

A migration imaging system capable of producing high quality images of high density, continuous tone and high resolution has been developed. Such imaging systems are disclosed in copending US. patent application Ser. No. 837,780 and Ser. No. 837,591, both filed June 30, 1969, both of which the entire contents of which are hereby incorporated herein by reference In a typical embodiment of these migration imaging systems, an imaging member comprising a substrate, a layer of softenable material comprising electrically photosensitive migration material is latently imaged, e.g., by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation, such as light. When the photosensitive migration material is originally in the form of a fracturable layer located at the upper surface of the softenable material, particles of the migration material in the exposed areas of the member migrate toward the substrate when the member is developed by decreasing the resistance of the softenable layer sufficient to allow migration of the migration material in depth in the softenable material.

Various methods for developing, i.e., reducing the resistance of the softenable material to migration of the migration material, of latently imaged migration imaging members and migration imaging systems are known. These various development modes include solvent wash-away and softening the softenable material, e.g., by solvent vapor softening, heat softening and combinations thereof, as well as other methods of reducing the resistance of the softenable material to allow migration of the migration material in depth in the softenable material.

The imaging system disclosed in copending application Ser. No. 460,377, filed June 1, 1965, the entire contents of which is hereby incorporated by reference, generally comprises a combination of process steps which include forming a latent image on a migration imaging member and developing with solvent liquid or vapor or heat or combinations thereof, to render the latent image visible. In certain methods of forming the latent image, non-photosensitive r photosensitively inert, fracturable layers and particulate material may be used to form images. as described in copending application Ser. No. 483,675, filed Aug. 30, I965, the en tire contents of which is incorporated herein by reference, wherein a latent image is formed by a wide variety of methods including charging in imagewise configuration through the use of a mask or stencil; first forming such a charge pattern on a separate photoconductive insulating layer according to conventional xerographic reproduction techniques and then transferring this charge pattern to an imaging member by bringing the two layers into close proximity and utilizing breakdown techniques as described, for example, in Carlson,

US. Pat. No. 2,982,647 and Walkup, US. Pat. Nos. 2,825,814 and 2,937,943.

Once a migration imaging member has been developed, i.e., the resistance of the softenable material reduced sufficiently to allow migration of the migration material in depth in the softenable material, and the material has, in fact, migrated, then the background material, i.e., the unmigrated migration material, normally has to be removed so that a more acceptable image is present.

The instant invention removes the background by the process of agglomerating the background material while simultaneously allowing this background material to migrate in depth in the softenable material. Once the background material has been agglomerated, the member becomes transparent in these areas resulting in a relatively background free, heat developed, migration imaged member.

SUMMARY OF THE INVENTION It is, therefore, an object of the invention to provide a method of removing background from heat developed migration imaging members.

It is further an object of this invention to provide a method of simultaneously agglomerating and migration the unexposed migration material in depth in the softenable material during the heat development step.

The foregoing objects and others are accomplished by providing an imaging member comprising a substrate, a layer of softenable material overlying the substrate, the softenable material containing a layer of photosensitive migration material contiguous the surface of the softenable material opposite the substrate and contacting the softenable material. The softenable material is capable of being heated sufficiently to allow migration of the migration material in depth in the softenable material. Furthermore, an overlayer of material is placed on the softenable layer which comprises a partially esterfied rosin polymer. Process steps comprise uniformly negatively charging the member, heating the member sufficiently to allow substantially all of the negative charge on the surface of the overlayer to migrate in depth in the overlayer but the heating is not sufficient to allow migration of the migration material in depth in the softenable material. After the heating step, the member is cooled to its original temperature. The member is then uniformly negatively charged a second time and imagewise exposed to activating electromagnetic radiation. The member is then developed by heating sufficiently to allow imagewise migration through the softenable material to the substrate of the imagewise exposed migration material while the migration material in the unexposed areas is simultaneously agglomerated and migrated in depth in the softenable material thereby removing the background, i.e., rendering the background substantially transparent.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects and further features thereof, reference is now made to the following detailed disclosure of this invention taken in conjunction with the accompanying drawings wherein:

FIG. I is a partially schematic drawings of a layer configuration migration imaging member with an overlayer of material.

FIG. 2 is a partially schematic drawing representing charging with a corotron charging device of a layer configuration migration imaging member containing an overlayer of material.

FIG. 3 represents a negatively charged migration imaging member containing an overlayer.

FIG. 4 is a partially schematic drawing of heating the member to allow charge to migrate into the overlayer of material but not sufficient to allow migration of migration material.

FIG. 5 is a partially schematic drawing illustrating recharging a migration imaging member.

FIG. 6 is a partially schematic drawing representing imagewise exposing a layer configuration migration imaging member.

FlG. 7 is a partially schematic drawing of a developed member of the instant invention illustrating the imagewise migration of the imagewise exposed migration material to the substrate and the simultaneous agglomera tion and migration of the unexposed background migration material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 which shows a partial schematic drawing of a layer configuration migration imaging member with an overlayer of material. Imaging member 1 comprises a substrate 5 and a layer of softenable material 4 overlying substrate 5. Softenable material 4 contains a layer of photosensitive material 3 which is contiguous the surface of the softenable material opposite substrate 5 and contacting softenable material 4. ()verlying softenable layer 4 is overlayer 2 which comprises a partially esterfied rosin polymer.

Overlayer 2 may comprise any partially esterfied rosin polymer, preferably Pentalyn 255 resin, a partially esterfied rosin polymer, available from Hercules Co., Inc. Such materials also include Staybelite Ester 10, a partially hydrogenated rosin ester; Floral Ester, a hydrogenated rosin triester; all from Hercules Powder Co.

The thickness of layer 2 is preferably from about 0.01 to about 2.0 microns thick. More preferably, layer 2 is about 1.0 micron thick.

Overlayer 2 may also be transparent, translucent or opaque, depending upon the imaging system in which the overcoating member is desired for use. Where the overlayer comprises substantially electrically insulating material, it will typically have resistivities not less than about 10 ohms-cm., and preferably have resisitivites of not less than about 10 ohms-cm. Overlayer 2 is typically preferably of a thickness up to about 75 microns, although thicker overlayers may be suitable and desirable in certain embodiments. More preferably, the thickness of the overlayer generally should range from about 0.01 to about 2.0 microns. A preferred range of thickness which yields outstanding results is about 0.1 micron. Furthermore, the material must have the ca pacity of when heated to allow charge, which is deposited on its surface, to migrate in depth in this overlayer Migration material 3 should be substantially insoluble in the softenable material and otherwise not adversely reactive therewith.

Photosensitive materials for layer 3 permit the imaging member hereof to be imaged by the optimum electrically optical mode hereof, to be further described, which is a simple, direct, optical sensitive method of producing high quality images. Typical such photosensitive materials include inorganic or organic photoconductive insulating material; materials which undergo conductive changes when photoheated, for example, see Cassiers, Photog. Sci. Engr. 4 No. 4, 199 1960); materials which photoinject or inject when photoheated.

While photoconductive particles (and photoconductive") is used in its broadest sense to mean materials which show increased electrical conductivity when illuminated with electromagnetic radiation and not necessarily those which have been found to be useful in xerography in a xerographic pigment-binder plate configuration) have been found to be a class of materials useful as electrically photosensitive materials in this invention and while the photoconductive effect is often sufficient in the present invention to provide an electrically photosensitive" material, it does not appear to be a necessary effect. Apparently, the necessary effect according to the invention, is the selective relocation of charge into, within or out of the material or particles, said relocation being effected by light acting on the bulk or the surface of the electrically photosensitive material, said relocation occurring before or during development, by exposing said material or particles to activating radiation which may specifically include photoconductive effects, photoinjection, photoemission, photochemical effects and others, which cause said selective relocation of charge.

When migration layer 3 comprises particles, a preferred average particle size is from about 0.01 to about 2.0 microns. Layers of particle migration material preferably should have a thickness ranging from about the thickness of the smallest element of migration material in the layer to about twice the thickness of the largest element in the layer. it should be recognized that the particles may not all be packed tightly together laterally or vertically so that some of the thickness of layer 3 may constitute softenable material.

Softenable layer 4, may be any suitable material, typically a plastic or thermoplastic material, which is capa ble of having its resistance to migration reduced sufiiciently to allow migration of the migration material in depth in the softenable material. Softenable layer 4 is also capable of allowing simultaneous agglomeration and migration in depth in the softenable material of the unexposed background migration material. Furthermore, as a specific preferred embodiment of development, softenable material should be capable of being softened by heat sufficient to allow imagewise migration through the softenable material to the substrate of the imagewise exposed migration material. Preferably, the softenable material should have a softening range of at least about 10C. and an initial softening point of less than about C. and a surface melt viscosity in the range between 10 to l0 poise.

Softenable" as used herein to depict softenable layer 4, is intended to mean any material which can be rendered by the development step thereof, i.e., heat, more permeable to particles migrating through its bulk.

Typically, preferred substantially electrically insulating softenable material includes a host of plastic and thermoplastic material, examples of which are specifically recited in copending application Ser. No. 837,780, filed June 30, 1969, the entire contents of which is hereby incorporated by reference; paraffins and waxes and other materials which are typically substantially electrically insulating and capable of having its resistance to migration reduced sufficiently to allow migration of the migration material, may be used in the advantageous system of the present invention. Such substantially insulating softenable materials will typically have resistivities not less than about ohms cm., and preferably have resistivities not less than about IO ohms-cm.

Especially preferred substantially electrically insulating softenable materials include copolymers of styrene and hexylmethacrylate; copolymers of styrene and n-butylmethacrylate; copolymers of styrene and octylmethacrylate; copolymers of styrene and t-decylatesstyrene and copolymers of methyl methacrylate and tdecylate-styrene.

Softenable layer 4 may be any suitable thickness with preferred thickness from about one-half to 16 microns.

Substrate 5 may be electrically conductive or insulating. Also, substrate 5 may be photosensitive or nonphotosensitive. Conductive substrates generally facilitate the charging or sensitizing of the member and typically may be of copper, brass, rickel, zinc, chromium, stainless steel, conductive plastics and rubbers, aluminum, steel, cadium, silver, gold or paper rendered conductive by the inclusion of a suitable chemical therein or through conditioning in a humid atmosphere to insure the presence therein of sufficient water content to render the material conductive. Suitable substrates are disclosed in copending U.S. patent application Ser. No. 837,780, filed June 30, 1969, the entire contents of which are hereby incorporated by reference herein.

Referring now to FIG. 2, wherein the imaging member contains layer 3 which comprises photosensitive material which is being uniformly negatively charged. In FIG. 2, the imaging member is being uniformly elec trostatieally charged, illustratively by means of a corona discharging device 6 which is shown to be transversing the member from left to right depositing a uniform, illustratively negative charge on the surface of overlayer 2. Corona discharging devices of the general description and general operating procedures as disclosed in Vyverberg Pat. No. 2,836,725 and Walkup, U.S. Pat. No. 2,777,957 have been found to be useful in discharge of member 1. Other charging techniques and other corona discharging devices are described in copending application Ser. No, 837,780, filed June 30, 1969.

Referring now to FIG. 3 which illustrates member 1 with a uniform negative charge on the surface of overlayer 2.

Referring now to FIG. 4, overlayer 2 is heated suffciently by heating element 10 to allow substantially all of the negative charge on the surface of overlayer 2 to migrate in depth in overlayer 2. However, the heating in this step is not sufficient to allow migration of migration material 3 in depth in softenable layer 4.

Heating element 10 may be any device which is capable of heating the member, i.e., overlayer 2, sufficiently to allow migration of negative charge into layer 2.

The member, i.e., overlayer 2, is cooled to its original temperature or to at least a temperature which is sufficiently low enought so that the negative charge depos ited during the second charging step will not migrate into overlayer 2 but will remain on the surface of over layer 2 as illustrated in FIG. 5.

Referring now to FIG. 5, imaging member 1 is uniformly electrostatically charged, illustratively by means of a corona charging device 6 which is shown to be transversing the member from left to right and depositing a uniform, illustratively negative charge on the surface of layer 2 for a second time.

Referring now to FIG. 6 which illustrates a uniform negative charge which has migrated in depth in overlayer 2 and is shown to be contiguous the interface between overlayer 2 and the layer of migration material 3 contained in softenable material 4. Further illustrated is a uniform negative charge on the surface ofoverlayer 2. This charge does not migrate during this particular step, since the member was cooled, i.e., returned to its original temperature after the heating step, in order to prevent migration of this charge at this timev After the second charging step, member I is exposed to an imagewise pattern of activating electromagnetic radiation 7. For purposes of illustration, the negative charges at the interface of overlayer 2 and migration layer 3 are depicted as having moved into migration layer 3 in the illuminated areas.

Referring now to FIG. 7, the application of heat a means for softening the softenable material of softenable layer 4 to allow migration of migration material 3, may be used to develop imaging member I, whereby migration material 3, in the imagewise exposed areas, migrates through softenable material 4 to substrate 5 and the unexposed migration material, i.e., background migration material, simultaneously agglomerates and migrates in depth in the softenable material during this development step. These agglomerates of migrating migration material are illustrated as agglomerates 9 in FIG. 7.

It is believed that the imagewise exposed migration material moves very quickly, i.e., migrates, through softenable material 4 and dispersed quickly in softenable material 4 and deposits on substrate 5 an image configuration 3a before any agglomeration takes place, This process of migrating quickly and dispersing quickly in the softenable material by the imagewise exposed migration material 3u, it is believed, prevents this material from agglomeratingv However, it is believed that the unexposed areas, i.e., background areas of mi gration material, migrate much more slowly and, therefore, are allowed to agglomerate, as illustrated as ag glomerating in FIG. 7, while they are migrating through the softenable material. It is believed that these unexposed migration particles, even though they do not directly attach themselves to charges as do the particles in the imagewise exposed areas, are driven by charges which are contained in overlayer 2 which continues to supply charges to agglomerated particles 9 and, therefore, particles 9 continue to slowly migrate. It is further believed that particles 9 do not migrate as quickly as migration particles 3a in the imagewise exposed areas since, as illustrated in FIG. 6, the electrical charges are depicted as having moved into the migration particle layer 3 in the imagewise exposed areas and this, it is believed, causes these particles to move very quickly when softenable material 4 is softened sufficiently to allow migration of these particles. As illustrated in FIG. 7, the imaged member comprises imagewise migrated particles 30 on the surface of substrate 5, i.e., these particles have migrated through the softenable material and are resting on substrate 5 and also illustrates the unexposed, i.e., background particles 9, which have simultaneously agglomerated and are migrating in depth in softenable layer 4. Therefore, imaged member 8 illustrates a migration imaging member which has a dense imagewise pattern of particles 3a with a relative transparent background, since the background particles 9 have agglomerated.

The following examples further specifically define the present invention. The parts and percentages are by weight unless otherwise indicated. All exposures are from a tungsten filament light source, unless otherwise specified. The examples below are intended to illustrate various preferred embodiments of the instant invention. The examples are directed to heat development migration imaging members.

EXAMPLE l An imaging member is produced by preparing a softenable material comprising about a 12 weight percent solution of a custom sensitized 80/20 mole percent copolymer of styrene and hexylmethacrylate having a molecular weight of about 41/300, intrinsic viscosity in toluene at about 25C. of about 0.16. The softenable material is then coated onto an aluminized Mylar substrate with a gravure roller and then allowed to dry. The softenable material has a thickness of approximately 2 microns. The surface of the softenable material is then coated with amorphous selenium by the vac uum deposition process as fully described in copending application Ser. No. 813,345, filed Apr. 3, 1969. Vacuum evaporation of selenium onto the softenable layer results in a layer of particulate selenium being formed, having average particle size of about 0.7 micron. This member, i.e., the surface of the softenable material containing the layer of particulate selenium, is then overcoated with a 1 micron thick layer of Pentalyn 250 resin, :1 partially esterfied rosin polymer available from Hercules Powder Co., with a gravure roller and then allowed to dry. This member is uniformly electrostatically charged using a corona device to a surface potential of negative 200 volts in the dark. The member is then heated for seconds at l C. to allow this negative charge to migrate to the overlayer-softenable material interface. i.e., the surface of the softenable material containing the layer of selenium. The member is then cooled to ambient temperature, i.e., the temperature before the heating step, while still maintaining the member in the dark. The member is again uniformly electrostatically charged using a corona device to a surface potential of negative 200 volts, and imagewise exposed to activating radiation, here light, of approximately 5 ergs/cm' of 4,000 angstroms light through a photographic transparency in contact with the member. The member is then heated to 100C. for secends. The previously exposed areas migrate through the softenablc material and to the substrate and the previously unexposed areas simultaneously agglomerate and migrate in depth in the softenable material. An excellent imaged member is obtained by heat development with relatively no background material observable. Therefore. the density in the background areas is substantially lower because of the agglomeration of the selenium particles in this area and, therefore, the background areas appear transparent. However, in the exposed areas there is a dense bluish image. The bluish color of the imagewise migrated particles indicate that the particles, in image configuration, have migrated and dispersed in the softenable material and have not agglomerated.

What is claimed is:

I. An imaging method comprising:

a. providing an imaging member comprising a substrate, a layer of electrically insulating softenable material overlying said substrate, said softenable material containing a layer of electrically photosensitive migration material contiguous the surface of said softenable material opposite said substrate and contacting said softenable material, said softenable material capable of being heated sufficiently to allow migration of said migration material in depth in said softenable material and an overlayer of material on said softenablc layer com prising a partially esterfied rosin polymer;

b. uniformly negative charging said member;

0. heating said member sufficiently to allow substantially all of the negative charge on the surface of said overlayer to migrate in depth in said overlayer but said heating not sufficient to allow migration of the migration material in depth in said softenable material;

d. after step (c), cooling said member to a temperature which will not allow migration of charge in depth in said overlayer;

e. after steps (b), (c) and (d), uniformly negatively charging said member;

f. imagewise exposing said member to activating electromagnetic radiation; and

g. heating said member sufficient to allow imagewise migration of the imagewise exposed migration material through the softenable material to the substrate and to allow simultaneous agglomeration and migration in depth in the softenable material of the unexposed migration material.

2. The method according to claim I wherein the heating of step (c) is from about C. to about C. for about 1 to 10 seconds.

3. The method according to claim 2 wherein the heating of step (c) is about 1 10C. for about 5 seconds.

4. The method according to claim 1 wherein the photosensitive material is photoconductive.

5. The method according to claim 1 wherein the overlayer is from about 0.01 to about 2.0 microns thick.

6. The method according to claim 5 wherein the overlayer is about 1.0 micron thick. 

1. AN IMAGING METHOD COMPRISING: A. PROVIDING AN IMAGING MEMBER COMPRISING A SUBSTRATE,A LAYER OF ELECTRICALLY INSULATING SOFTENABLE MATERIAL OVERLYING SAID SUBSTRATE, SAID SOFTENABLE MATERIAL CONTAINING A LAYER OF ELECTRICALLY PHOTOSENITIVE MIGRATION MATERIAL CONTIGUOUS THE SURFACE OF SAID SOFTENABLE MATERIAL OPPOSITE SAID SUBSTRATE AN CONTACTING SAID SOFTENABLE MATERIAL, SAID SOFTENABLE MATERIAL CAPABLE OF BEING HEATED SUFFICIENTLY TO ALLOW MIGRATION OF SAID MIGRATION MATERIAL IN DEPTH IN SAID SOFTENABLE MATERIAL AND OVERLAYER OF MATERIAL ON SAID SOFTENABLE LAYER COMPRISING A PARTIALLY ESTERFIED ROSIN POLYMER, B. UNIFORMLY NEGATIVE CHARGING SAID MEMBER C. HEATING SAID MEMBER SUFFICIENTLY TO ALLOW SUBSTANTIALLY ALL OF THE NEGATIVE CHARGE ON THE SURFACE OF SAID OVERLAYER TO MIGRATE IN DEPTH IN SAID OVERLAYER BUT SAID HEATING NOT SUFFICIENT TO ALLOW MIGRATION OF THE MIGRATION MATERIAL IN DEPTH IN SAID SOFTENABLE MATERIAL, D. AFTER STEP (C) COOLING SAID MEMBER TO A TEMPERATURE WHICH WILL NOT ALLOW MIGRATION OF CHARGE IN DEPTH IN SAID OVERLAYER, E. AFTER STEPS (B), (C) AND (D), UNIFORMLY NEGATIVELY CHARGING SAID MEMBER, F. IMAGEWISE EXPOSING SAID MEMBER TO ACTIVATING ELECTROMAGNETIC RADIATION, AND G. HEATING SAID MEMBER SUFFICIENT TO ALLOW IMAGE WISE MIGRATION OF THE IMAGEWISE EXPOSED MIGRATION MATERIAL THROUGH THE SOFTENABLE MATERIAL TO THE SUBSTRATE AND TO ALLOW SIMULTANEOUS AGGLOMERATION AND MIGRATION IN DEPTH IN THE SOFTENABLE MATERIAL OF THE UNEXPOSED MIGRATION MATERIAL.
 2. The method according to claim 1 wherein the heating of step (c) is from about 100*C. to about 120*C. for about 1 to 10 seconds.
 3. The method according to claim 2 wherein the heating of step (c) is about 110*C. for about 5 seconds.
 4. The method according to claim 1 wherein the photosensitive material is photoconductive.
 5. The method according to claim 1 wherein the overlayer is from about 0.01 to about 2.0 microns thick.
 6. The method according to claim 5 wherein the overlayer is about 1.0 micron thick. 